DESCRIPTION (Adapted from the Investigator?s Abstract): The goal of this two year project is to determine the sequence of the chromosome of the human oral bacterium Actinomyces naeslundii. A. naeslundii is the most prominent actinomyces sp. found in humans where its niche is almost exclusively the oral mucosa and root surfaces. A. naeslundii colonizes humans in the first few days postpartum to become an important component of the oral biofilm. The bacterium is a significant portion of the flora of healthy adults but it can also act as part of the matrix that is necessary for infection by specialized oral pathogens. The A. naeslundii strain to be sequenced is an isolate called MG1, which is the prominent A. naeslundii genospecies found in humans, and is also a strain that can be genetically manipulated. This stain?s genome is estimated to be approximately 6.7 Mb. Small, medium and large insert libraries will be end sequenced to provide approximately 8X genome coverage. After alignment of about 100,000 sequencing reads using the TIGR assembler program, gaps will be filled in by directed PCR of genomic DNA. With generation of these clones and determination of the complete genome sequence, similarities in genes among other bacteria or in gene databases will be established using appropriate computer-assisted approaches, providing a working knowledge of absent or supplemental genetic components. These data will lead to the identification of novel genes of A. naeslundii potentially involved in attachment and colonization to human tissue, genes important in the pathogenesis of infections caused by the bacterium and determinants for surface proteins that are candidate targets for vaccines and other therapeutic interventions. In particular, this project will greatly aid in understanding the vital role A. naeslundii plays in the early colonization of the human oral cavity and in biofilm formation through interactions with other oral bacteria.